Mark C. Petri

Temperature gradient driven constituent redistribution in UZr alloys

Abstract Although the phenomenon of constituent redistribution is common in UPuZr alloys irradiated under a wide range of conditions, it has been observed in UZr alloys only at elevated temperatures. Redistribution is relatively rapid and is essentially complete by 5 at% burnup. Experimental observations of constituent redistribution in UZr fuel elements are presented and analyzed. A model based on a thermal diffusion mechanism is proposed, and its computer implementation is described. The model calculations, supported by experimental observation, indicate that the excess enthalpy of solution of the bcc γ-phase controls the redistribution process as an additional driving force. A heat of transport of −50 to −100 kJ/mol in this phase results in the best match between calculation and experimental observations. The model predicts that constituent redistribution will be observed only when a region of the fuel operates at temperatures above 935 K.

Interdiffusion behavior in UPuZr fuel versus stainless steel couples

Abstract Irradiation of metallic UZr or UPu-Zr nuclear fuel alloys in a reactor results in fuel swelling that can lead to interactions between the fuel and cladding steel. These interactions are complicated, involving many variables and producing complex microstructures. This paper contributes to the understanding of fuel-cladding interaction by reporting results from diffusion couples annealed at 650°C for 100 h between a UPuZr alloy and stainless steels with and without Ni. SEM-EDX analyses of these couples were utilized to determine the composition of phases throughout the diffusion zone and to generate composition profiles. Overall, a diffusion couple between a UPuZr fuel alloy and a cladding steel that does not contain Ni develops the largest diffusion zone of any of the fuel-cladding steel diffusion couples; a slightly smaller diffusion zone develops for a couple between a UPuZr alloy and a cladding steel containing Ni. By comparing these results with those from earlier binary fuel studies, it is concluded that the presence of Pit increases interdiffusion of the various components in fuel-cladding steel diffusion couples.

US work on technical and economic aspects of electrolytic, thermochemical, and hybrid processes for hydrogen production at temperatures below 550°C

Hydrogen demand is increasing, but there are few options for affordable hydrogen production free of greenhouse gas emissions. Nuclear power is one of the most promising options. Most research is focused on high-temperature electrolytic and thermochemical processes for nuclear-generated hydrogen, but it will be many years before very high temperature reactors become commercially available. For light water reactors or supercritical reactors, low-temperature water electrolysis is a currently available technology for hydrogen production. Higher efficiencies may be gained through thermo-electrochemical hydrogen production cycles, but there are only a limited number that have heat requirements consistent with the lower temperatures of light-water reactor technology. Indeed, active research is ongoing for only three such cycles in the USA. Reductions in electricity and system costs would be needed (or the imposition of a carbon tax) for low-temperature water electrolysis to compete with todays costs for steam methane reformation. The interactions between hydrogen and electricity markets and hydrogen and electricity producers are complex and will evolve as the markets evolve.

Isothermal diffusion in uranium-plutonium-zirconium alloys

Abstract Isothermal diffusion couple experiments were performed at 1023 K to investigate diffusion phenomena in body-centered cubic UPuZr alloys. The UPuZr alloys covered the uranium-rich corner of the ternary phase diagram with plutonium concentrations up to 27 at.% and zirconium concentrations up to 20 at.%. Ternary interdiffusion coefficients were calculated at the common composition between two couples with intersecting diffusion paths. The cross interdiffusion coefficient for zirconium ( D ZrPu U ) is negative and has a magnitude twice that of the main coefficient ( D ZrZr U ). In contrast, D PuZr U is negligible compared with D PuPu U , D PuPu U is an order of magnitude greater than D ZrZr U . Average effective interdiffusion coefficients were determined for all components over concentration ranges on the two sides of the Matano plane as well as for the entire diffusion zone of the couples. In general, these coefficients increase with increasing plutonium concentration and decrease with increasing zirconium concentration.

Uranium-plutonium interdiffusion at 750°C

Abstract An isothermal diffusion couple between pure uranium and a uranium-27 at% plutonium alloy was annealed at 750°C for 25 h. Composition profiles were determined from electron microanalyses, from which interdiffusion fluxes and interdiffusion coefficients were evaluated. The presence of plutonium greatly increases diffusion at this temperature over what would be predicted from uranium self-diffusion studies. Moreover, diffusivities in the body centered cubic U(γ) phase increase with increasing plutonium concentration, unlike interdiffusion in the orthorhombic U(α) phase at lower temperatures. The diffusion results suggest that plutonium has a greater intrinsic diffusivity than uranium at 750°C.

Phase identification in a U–Zr/Ni–Cr diffusion couple using synchrotron radiation

The diffusion zone between a U-23 at.{percent} Zr alloy and a Ni-16.4 at.{percent} Cr alloy exhibited nine distinct phase layers, many of which were mixtures of two phases. Four single-phase regions were less than 10 {mu}m wide. To identify these phases by diffractometry, a synchrotron x-ray beam was collimated by a 50 {mu}m by 1 mm slit. This beam was translated across the sample to obtain diffraction patterns throughout the diffusion zone. In this way, only a few phases were simultaneously within the beam, easing identification of the phases. Strains in the lattice due to solid solution were also observed. These microdiffraction techniques are applicable to a wide range of material systems. {copyright} {ital 1996 Materials Research Society.}

A summary of the Third Information Exchange Meeting on the nuclear production of hydrogen

The Nuclear Energy Agency of the Organisation for Economic Co-operation and Development has organised three international exchange meetings on hydrogen production through nuclear power. The most recent meeting was held in October 2005 in Oarai, Japan, and was sponsored by the International Atomic Energy Agency. The two-and-a-half-day conference covered a full range of topics related to the nuclear production of hydrogen. Presentations were made and discussions were held on the economic prospects of a hydrogen economy and nuclear powers potential role in it, global research and development activities related to hydrogen production technologies, the coupling of hydrogen production facilities to nuclear heat sources, and basic and applied science supporting nuclear hydrogen generation. The meeting presentations are available at: http://www.nea.fr/html/science/hydro/iem3/.

U.S. Department of Energy sponsored in-depth safety assessments of VVER and RBMK reactors.

Throughout the 1990s the National Nuclear Security Administration of the U.S. Department of Energy has worked to build capability in countries of the former Soviet Union to assess the safety of their VVER and RBMK reactors. Through this Plant Safety Evaluation Program, deterministic and probabilistic analyses have been used to provide a documented plant risk profile to support safe plant operation and to set priorities for safety upgrades. Work has been sponsored at fourteen nuclear power plant sites in eight countries. The Plant Safety Evaluation Program has resulted in immediate and long-term safety benefits for the Soviet-designed nuclear plants.Copyright

Application of quantum beams to analysis of radioactive materials

Abstract The methodology of quantum beams, an X-ray beam in this study, was used to examine the diffusion layer between a U-23 at.% Zr alloy and a Ni-16.4 at.% Cr alloy that exhibited nine distinct layers, many of which were mixtures of two phases. Four single-phase regions were less than 10 μm wide. A synchrotron X-ray beam, collimated by a 50 μm by 1 mm slit, was used to identify these phases. This beam was translated across the sample to obtain diffraction patterns throughout the diffusion zone. In this way, only a few phases were simultaneously within the beam, easing identification of the phases. Strains in the lattice due to solid solution were also observed. These microdiffraction techniques are applicable to a wide range of material systems.

Hard x-ray microanalytical beam line at the CAMD synchrotron

Argonne National Laboratory (ANL) is collaborating with Louisiana State University (LSU) in constructing a synchrotron x-ray micro-analytical beamline at the Center for Advanced Microstructures and Devices (CAMD) in Baton Rouge, Louisiana. This project grew from earlier work at the National Synchrotron Light Source (NSLS), where a team of ANL researchers developed techniques to examine small-scale structures in diffusion zones of a variety of materials. The ANL/CAMD beamline will use x-ray fluorescence, diffraction, and absorption spectroscopy techniques to reveal both compositional and structural information on a microscopic scale.